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4- SUMMARY AND CONCLUSIONS4.1. Summary:1- A literature survey has been presented including a historical statement about the alkali aggregate reactions (ACR) in concrete. The alkali origin and their limits in concrete have been declared. The types of ACR and the factors controlling each process2- The current study have been divided into two main sections investigating:a- The alkali– carbonate reactions (ACR) in low dolomite rocks.b- The alkali–carbonate reactions (ACR) in high and medium dolomite rocks.3- In the first section, the chemical, physical, mechanical and mineralogical characteristics as well as the potential alkali reactivity of low have been investigated. This part of the study investigated the expansion of mortar under the effect of alkali * The presence of admixed alkali accelerates the mortar expansion relative to the alkali–free specimens.* The combination of external alkali together with elevated temperature (80oC) comprises a severe regime that enhances the expansion. However, the expansion values reached – even after 90 days exposure – are still below the value proposed by ASTM C1260 (i* low dolomite incorporating weathering alteration products is more prone to alkali expansion.* ACR can be thermally activated.The compressive strength of mortars or concrete utilizing low dolomite aggregate as affected by admixed alkali has been determined. It has been found that, the alkali presence in concrete, although causing an initial strength gain in the early ages (actinThe effect of some supplementary cementing materials (SCM’s) on alkali–carbonate reactivity has been, also, investigated. The used SCM’s were:- 10 and 20% silica fume.- 10 and 20% fly ash.- 10 and 20% rice husk ash- 10 and 20% homraThe performance of these SCM’s has been evaluated through monitoring the linear expansion of mortar bars. It has been found that:* 10% silica fume seems sufficient to control expansion due to (slightly–moderately) reactive dolomite aggregates.* The use of 10–20% fly ash is highly effective in controlling expansion due to low dolomite aggregates.*Replacing ordinary Portland cement by blast furnace slag cement. (> 35% slag) yield noticeable reduction in the expansion due to carbonate aggregates.* Replacing ordinary Portland cement by sulphate resistance cement gives high reduction in the expansion due to carbonate aggregates with SRC more than in SC and more than in OPC. This mainly due to C3A in SRC not more than 2, so the compressive strength 4- In the second section of the current study, three types of carbonate rocks, namely, medium dolomite (MD) and high dolomite (HD) have beenused for mortar preparation. The chemical, physical, mechanicaland mineralogical composition, of these carbonates have been determined. These properties directed the study to focus on investigating the behavior of both calcitic dolomite and dolomite since they exhibit better physical and mechanical properties than caThe linear expansion of mortar bars containing HD and MD aggregates admixed with 1.5% Na2O equivalent at 100% R.H. or immersed in 1N NaOH solution at 80oC has been determined. The mortar expansion values in case of both aggregates have been found insignifCompressive strength measurements revealed that the mortar incorporating dolomite aggregate retains higher strength levels than that incorporating calcitic dolomite aggregate. Compressive strength development of both mortar types could not resist the hot The effect of exposure to saline media on the ACR has been investigated. Mortar cubes manufactured using dolomite aggregates have been exposed to aggressive chloride and sulfate media, namely, 1N of each of Na2SO4, NaCl, Mg SO4 and MgCl2 solutions at 80oC20% fly ash > 20% silica fume > 20% RHA > 20% homra >10% fly ash >10% silica fume > 10% RHA
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